From a user: 

I have a column chart with months from a Purchase Date dimension on the axis panel and a Sales measure as the series.

Question 1:

How do I create a formula to calculate the average sales per day, for each month?

Answer 1:

Full explanation can be found here: http://community.sisense.com/forums/p/101/162.aspx#162

Question 2:

After creating such a formula, how can I add it to the chart as a line (so the average sales measure appears as a line chart, while the sales measure remains a column chart)?

Answer 2:

* Add the new formula to the chart widget via the Widget Data Layout Editor.

* Right-click the chart and choose 'Format Chart...'

* Navigate to the 'Data Series Tab'

* Select the sales average measure in the 'Select Series' selection box

* Select 'Line' in the 'Display series as' selection box.

* Select ''Y2 Axis' in the 'Plot series on axis' selection box.

* Click OK.